Wheel loaders are generally vehicles with a work implement such as a loader or bucket on the front that can be raised and lowered to scoop up, carry and drop particulate material. They are called “wheel” loaders since they are supported on large steerable wheels. Many wheel loaders are articulated vehicles that steer by “bending” the frame and not by turning the wheels, front and/or rear, with respect to the frame. Articulated wheel loaders do not have a single frame to which the front and rear wheels are mounted, but have at least two sub-frames that are coupled together to pivot or articulate with respect to each other about a generally vertical axis. Hydraulic steering cylinders are positioned between the sub-frames to extend and retract to bend the articulated vehicle. An articulated wheel loader may also include more than one sub-frame, and sub-frames may be able to pivot with respect to each other about additional axes.
Wheel loaders, like skid-steer loaders and loader-backhoes, have a typical mode of operation. These loader vehicles commonly travel in a “Y” path. The loader vehicle advances in a first direction, scoops up a portion of material, then backs up while turning hard to the right (or left). The loader vehicle then moves forward while turning hard to the left (or right), then straightens the wheels out to travel straight forward to a second location where the work vehicle deposits the material, either in a pile or into another vehicle. The work vehicle then backs up while turning hard to the left (or right), then goes forward while turning hard to the right (or left), then straightens up to follow the reverse path back to the first location. The two locations are typically separated only by a short distance on a single construction site.
This back-and-forth motion between two locations that are quite close to one another, with several hard turns to the right and to the left, place significant forces on an articulated wheel loader. The operator must repeatedly and rapidly turn from lock-to-lock during each loading/unloading cycle. In a typical workday, and operator may repeat this turning process a few hundred times.
As one might expect, these repeated and extreme turns place a significant strain on an articulated vehicle as the steering cylinders reach the end of their travel and the front and rear frames of the vehicle bang against each other.
Therefore, what is needed is an improved articulated construction vehicle, such as a wheel loader, that reduces the shock load on the vehicle when the vehicle is turned to the extreme left and extreme right. It is an object of this invention to provide an improved steering cylinder for an articulated vehicle.